Nematic Excitonic Insulator in Transition Metal Dichalcogenide Moiré Heterobilayers.

We study the effect of interelectron Coulomb interactions on the displacement field induced topological phase transition in transition metal dichalcogenide moiré heterobilayers. We find a nematic excitonic insulator phase that breaks the moiré superlattice's threefold rotational symmetry and preempts the topological phase transition in both AA and AB stacked heterobilayers when the interlayer tunneling is weak, or when the Coulomb interaction is not strongly screened. The nematicity originates from the frustration between the nontrivial spatial structure of the interlayer tunneling, which is crucial to the existence of the topological Chern band, and the interlayer coherence induced by the Coulomb interaction that favors uniformity in layer pseudospin orientations. We construct a unified effective two-band model that captures the physics near the band inversion and applies to both AA and AB stacked heterobilayers. Within the two-band model the competition between the nematic excitonic insulator phase and the Chern insulator phase can be understood as the switching of the energetic order between the s-wave and the p-wave excitons upon increasing the interlayer tunneling.

Topological Phases in AB-Stacked MoTe_{2}/WSe_{2}: Z_{2} Topological Insulators, Chern Insulators, and Topological Charge Density Waves.

We present a theory on the quantum phase diagram of AB-stacked MoTe_{2}/WSe_{2} using a self-consistent Hartree-Fock calculation performed in the plane-wave basis, motivated by the observation of topological states in this system. At filling factor ν=2 (two holes per moiré unit cell), Coulomb interaction can stabilize a Z_{2} topological insulator by opening a charge gap. At ν=1, the interaction induces three classes of competing states, spin density wave states, an in-plane ferromagnetic state, and a valley polarized state, which undergo first-order phase transitions tuned by an out-of-plane displacement field. The valley polarized state becomes a Chern insulator for certain displacement fields. Moreover, we predict a topological charge density wave forming a honeycomb lattice with ferromagnetism at ν=2/3. Future directions on this versatile system hosting a rich set of quantum phases are discussed.

Interaction-Driven Filling-Induced Metal-Insulator Transitions in 2D Moiré Lattices.

Using a realistic band structure for twisted WSe_{2} materials, we develop a theory for the interaction-driven correlated insulators to conducting metals transitions through the tuning of the filling factor around commensurate fractional fillings of the moiré unit cell in the 2D honeycomb lattice, focusing on the dominant half-filled Mott insulating state, which exists for both long- and short-range interactions. We find metallic states slightly away from half-filling, as have recently been observed experimentally. We discuss the stabilities and the magnetic properties of the resulting insulating and metallic phases, and comment on their experimental signatures. We also discuss the nature of the correlated insulator states at the rational fractional fillings.

Lost region in amyloid precursor protein (APP) through TALEN-mediated genome editing alters mitochondrial morphology.

Alzheimer's disease (AD) is characterized by amyloid-ß (Aß) deposition in the brain. Aß plaques are produced through sequential ß/γ cleavage of amyloid precursor protein (APP), of which there are three main APP isoforms: APP695, APP751 and APP770. KPI-APPs (APP751 and APP770) are known to be elevated in AD, but the reason remains unclear. Transcription activator-like (TAL) effector nucleases (TALENs) induce mutations with high efficiency at specific genomic loci, and it is thus possible to knock out specific regions using TALENs. In this study, we designed and expressed TALENs specific for the C-terminus of APP in HeLa cells, in which KPI-APPs are predominantly expressed. The KPI-APP mutants lack a 12-aa region that encompasses a 5-aa trans-membrane (TM) region and 7-aa juxta-membrane (JM) region. The mutated KPI-APPs exhibited decreased mitochondrial localization. In addition, mitochondrial morphology was altered, resulting in an increase in spherical mitochondria in the mutant cells through the disruption of the balance between fission and fusion. Mitochondrial dysfunction, including decreased ATP levels, disrupted mitochondrial membrane potential, increased ROS generation and impaired mitochondrial dehydrogenase activity, was also found. These results suggest that specific regions of KPI-APPs are important for mitochondrial localization and function.